Confused on this really hard problem

Mathematics
Tutor: None Selected Time limit: 1 Day

At a party, everyone shook hands with everybody else. There were 66 handshakes. How many people were at the party?

Nov 7th, 2014

nC2 =66

n(n-1) =132

n^2 -n-132=-

n^2-12n+11n-132=0

n(n-12)+11(n-12)=0

(n-12)(n+11)=0

n=12  

n=-11  notadmissible

n=12

Nov 7th, 2014

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